Bottled water or tap? Whether we're on the go or stuck in one place for hours, we all need the answer to this question. Fortunately there is one: it's tap, filtered and in a stainless steel reusable bottle. Here's why:

1. Bottled water isn't strictly regulated.

Unlike municipal water utilities, bottled water companies are not required by law to publish safety test results of their water nor to disclose how their water is specifically treated or filtered.

2. Bottled water companies don't have to tell you exactly where the water comes from.

Some bottlers advertise their wares with images of pristine mountain streams, but the water they package is actually filtered tap water from a city water utility, its origins described in generic terms like "municipal water source."

3. Bottled water is more expensive.

A store-bought bottle of water can cost many times what it would cost you to filter it at home and pour it into your own reusable steel bottle.

The Pacific Institute calculates that it takes more than 17 million barrels of oil or the equivalent to produce all the plastic water bottles purchased in the U.S. a year.

Why should you use a stainless steel bottle?

Plastic reusable water bottles marked with recycle codes 3 or 7 can contain chemicals like the synthetic estrogen bisphenol A or its substitute bisphenol S. Both have been linked to hormone disruption.

The federal Food and Drug Administration doesn't require manufacturers of plastics used in packaging for food and drink to disclose the chemicals in their products. That regulatory gap leaves consumers are in the dark about what chemicals could leach into the water from plastic bottles. These could include formaldehyde, a known human carcinogen and acetaldehyde, a probable human carcinogen.

Aluminum water bottles are often lined with epoxy lacquer that contains BPA.

Traveling? You can't take a filled water bottle through security, but some airports like San Francisco International Airport, Washington, D.C.'s Reagan National airport and Atlanta's Hartsfield-Jackson airport have "filling" stations where you can top off your own reusable with filtered tap water.